Mechanical harvesters capable of uprooting and then denuding plants of their comestibles have vastly improved the speed and overall efficiency of the harvesting process. However, a major problem still attendant upon mechanical harvesting includes the initial sorting of comestibles from field debris and dirt clods. On the earliest harvesters, this primary sorting job was performed by a worker who visually examined the passing mixture of produce and debris and removed acceptable comestibles for further sorting. Manual sorting is not only labor consuming but also wastes produce that is discharged onto the ground before it can be manually removed from the transport conveyer.
When electronic sorters were first developed, colorimetry emerged as the most reliable and effective basis upon which to sort objects. The earliest colorimetry systems were monochromatic, but the later, more sophisticated systems used a bichromatic approach. Typical of these bichromatic systems are Swanson, U.S. Pat. No. 4,120,402 and Jones et al., U.S. Pat. No. 4,134,498. These systems use a source of constant light energy to bathe the subject materials. Then, dual detectors, each fitted with an appropriate filter, gather information regarding the reflected light. The dual detectors are interconnected to comparator circuitry which produces a reject signal if the input signals bear a predetermined relationship. The reject signal is fed to a powered ejector arm which deflects the unwanted object from the stream of articles.
The advantages of a bichromatic colorimetry sorter are manifest. The approach can be used for differentiating ripe from unripe comestibles, or organic from inorganic materials. Equally important, the signal to noise ratio afforded by the bichromatic system provides superior quality data for logic circuits to analyze than the monochromatic system, thus greatly increasing the reliability of the sorter apparatus.
Prior art bichromatic sorters do not perform well in separating organic from inorganic materials because the detectors used, generally photovoltaic silicon cells, are not sufficiently sensitive to the deep infrared light which inorganic materials reflect. Lead sulfide cells, however, perform well as deep infrared detectors, but have not been used successfully in prior art devices.
Changes in temperature drastically affect the resistance of the photoresistive lead sulfide cell. Variations between the temperaure sensitivity of individual cells result in different resistance values for a group of cells throughout a temperature spectrum. With the dual detector approach used in the prior art, temperature variations affect the relative resistance of two companion cells at differential rates. A relatively small change in ambient temperature demands recalibration of both detector circuits.
The requirement of frequent recalibration proved too time consuming and technically difficult to perform in the field. But without frequent recalibration, temperature variations encountered during in-field use of a dual detector sorter using lead sulfide detectors rendered the sorter unreliable and commercially unusable. Thus, the inability of prior art sorters to use the superior lead sulfide cell successfully stems from the use of two detectors to extract date from the reflected light.
The present invention, by changing the nature of the source of illumination, uses only one cell for detecting reflected light. Temperature variations do not degrade the reliability of the single detector cell system since the sensitivity of the material analysis circultry can readily be adjusted, if necessary, to compensate for temperature-dependent sensitivity variations in a single lead sulfide detector cell. Furthermore, for ripe/unripe sorting, the single detector cell system can be used to advantage with the lower sensitivity, silicon detector cell as well.
Thus, it is an object of the present invention to provide a colorimetric process for differentiating organic from inorganic materials or ripe from unripe comestibles using a sequentially ordered illumination source and a single detector cell.
It is another object to provide a colorimetry system which is bichromatic in nature, extremely responsive to the appropriate infrared spectrum for differentiating organic from inorganic materials or ripe from unripe comestibles, yet uses a single cell for detecting reflected light.
It is a further object to disclose a unique illumination system which produces a sequentially ordered band of light of alternating infrared frequencies.
It is yet another object of the present invention to provide sizing circuitry which works in conjunction with the rejection system to ensure consistent rejection of inorganic materials or unripe comestibles regardless of their size. These and other objects and advantages of the present invention will be fully discussed and explained in the detailed description contained herein.